Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$130.47	4.497%	$136.3372	$136.34	$136.35	$136.30
Purchase #2	$55.45	6.756%	$59.1962	$59.20	$59.20	$59.20
Purchase #3	$48.27	11.621%	$53.8795	$53.88	$53.90	$53.90
Purchase #4	$40.82	12.730%	$46.0164	$46.02	$46.00	$46.00
Purchase #5	$129.44	3.131%	$133.4928	$133.49	$133.50	$133.50
Purchase #6	$82.36	4.713%	$86.2416	$86.24	$86.25	$86.20
Purchase #7	$59.61	12.742%	$67.2055	$67.21	$67.20	$67.20
7 purchase totals =	$546.42		$582.3692	$582.38	$582.40	$582.30